If you want to get good at climbing, you have to contend with a very fundamental principle of the human body: tendons and ligaments respond to stress and get stronger much slower than muscles do. If you start to climb, and especially if you are a fit young person, your muscles get strong very quickly. Your tendons and ligaments will not, and eventually, you will pull harder with your muscles than your tendons and ligaments can take, and then they will break in some fashion. Tendons and ligaments also heal much slower than muscles do, and so these injuries will plague you for a long time. Months, or years, depending on how stupid you are when it comes to healthy recovery, and how useless your physical therapist is.

On the short-term timescale of rock climbing (1-2 years), this tendon/muscle healing imbalance means that trying to get better at pull-ups is stupid, because doing so will greatly increase your likelihood of injury. It also means that hangboard training is stupid, because you will strengthen your hand muscles and then tear a hand tendon. In fact, most any kind of upper-body strength training is stupid, because it will probably make you hurt yourself. On a longer timescale, upper-body strength training will be incredibly useful for improving rock climbing ability, but in the first two years of climbing, I think they can only lead to pain and frustration.

I think there are 4 things you can do to get better at climbing

1. Climb consistently. Go twice a week. Three times a week is probably too much. Your muscles will get strong too fast. Twice a week, very consistently, is your best bet.
2. Don't try very hard. This will be difficult, especially for fit competitive people climbing with each other, because you'll want to climb something harder than the others, or solve the problem first, or show off to some other attractive young person. But, if you try hard all the time, you will inevitably hurt yourself. Chill out. Climb as if you are a stoned sloth. No pressure. You can try hard once you are an actually good climber, and have strong connective tissue. Not till then.
3. Work on your footwork. Watch what the good climbers do with their feet, and imitate it. Never let a foot slip off a hold. If you do, it is your fault. The hold wasn't too slippery, you simply put the wrong pressure there. You can always improve your footwork.
4. Do yoga. For any situation or time in life, doing yoga will make you a healthier and happier human being, and climbing is no exception. Moving through the ranges of motion that you rarely exercise, stretching your tissues, getting better control of your limbs, this will all help your climbing immensely. Always fucking do yoga. No matter what else is happening in life.

That's it. You want to get good at climbing? Cool. It's a great sport, and a ton of fun. Resign yourself to the long haul, and for two years, go climb twice a week, don't try very hard, work on your footwork, and do yoga. After that, you'll be a formidable climber, probably won't be injured, and your connective tissue will be ready for you to start introducing advanced training stuff like tons of pull-ups and hang-boarding.

Now that I wrote them, these words are very obviously part of a larger storm of thoughts in my mind around ability and getting better at things and ignoring fucking moronic growth-hacking/shortcut-taking/silver-bullet-shooting mentalities and resigning yourself to The Long Game, where the real goodness in life comes from. At some point, I'll use this space to link to the other things I write on this greater meta-topic.

I've put a summary of my climbing history below, so you can understand how I came to these conclusions. I put it below so as to not bury the lede by an additional ~1000 words.

The first time I climbed was at a gym for a friend's birthday party. I was 9 or 10. I loved it. It was my favorite place to go in the world. I only went there 2 or 3 times for the next 5 years, because I was a kid and you can't do everything you want when you are a kid.

I started really climbing sometime early in high school, when an old teacher's husband took a friend and I climbing outdoors. It was cold, and my fingers didn't work very well, and I was terrible at it and didn't like it that much.

He took us climbing outdoors again some time later. It was warm out. My fingers worked way better, and I could get up routes, including routes that my friend could not. I thought "shit, I can actually do this". I liked that a lot, as up until then, I didn't feel like I was good at anything in life besides reading books. Whether or not that was actually true is a discussion for another time and place, but that is what I felt.

I climbed a lot once I got a car and a summer job. I went to the gym in a neighboring town, 30 minutes away. I found a group of kids from another neighboring town who climbed at this gym. They had a club, and went consistently a couple times a week with a teacher whose family I'd gone to church with earlier in life. I clicked with a few of these kids pretty well.

I climbed a lot. I started out going twice a week, but eventually, I was going 3 or 4 times a week. I'd get to the gym at 6 or 7, and stay till they closed at 10.

I got good at climbing. Not actually good, but good for how long I'd been doing it. I was light and fairly strong, and those two things help a lot. I started doing sets of pull-ups at the end of my gym sessions along with hangboard training to get stronger quicker.

I hurt myself climbing the first time 6 months after I started intensively gym climbing. I pulled or severely strained muscles or tendons between my shoulder blades. I lean towards tendons, because I couldn't climb afterwards without pain for a long time. It took 6 months to fully heal. Muscles don't take that long to heal.

I hurt myself climbing the second time 3 or 4 months after I started up intensively gym climbing after recovering from the first injury. I strained or tore or ruptured the ring & middle finger flexor tendons in one of my hands. I can no longer remember which one, left or right. This took another 6 months to heal, during which I did not rock climb at all.

I didn't climb much for a couple years after that. Then I got a job doing construction. Framing and siding. I'd come home from work and lay on the couch for an hour staring at the wall, too tired to move, finally get up the gumption to make dinner, then go to sleep. I got used to it after a couple of months, and had enough energy to go to the gym after work. I started climbing outdoors on the weekends. After 5 or 6 months of this, I was climbing the hardest things I'd ever climbed. I had a lot of fun.

I took a break for a month when I moved to attend a programming school in Portland, then found a gym nearby and started going a couple times a week after class.

I hurt myself climbing for the 3rd time two months after starting up at the gym in Portland. I was reaching through under my right arm with my left, and felt something go on the backside of my left shoulder. Rotator cuff. I tore it in some way, though I never found out where because I never got it scanned. I went to one PT appointment which was useless, and did a lot of weightlighting for a few months, which was not useless, and helped it to heal 100%. I hurt it again several years later jumping off a pickup, and it has given me problems ever since, but that second time was not a climbing injury.

I didn't climb after the first rotator cuff injury for a long time. Years. The wind was out of my climbing sails. I reasoned that since I had hurt myself 4-6 months after starting climbing, every time I started climbing, I was incapable of climbing without hurting myself. I didn't enjoy it anymore, because to me what was fun was getting better and seeing progress and climbing hard stuff, and every time I did that, I got hurt. Without fail, and on the same cadence. 4-6 months after starting. So what the hell was the point?

5 or 6 years later, I started going to a gym with a girl who I thought was cute. I hurt myself I think the second or third time we went. Middle and ring finger flexor tendons, again. Right hand. I heard a loud pop, and felt intense pain in my palm. I couldn't let her know that I'd done it, so I hid the pain and kept climbing, doing routes where it didn't hurt hardly at all. It's been 6 months since then, and this injury is still with me. I can't rock climb at all right now. Like I said above, tendons take a really really long time to heal.

At this point, what you might be thinking is: my god, what an absolute moron, how could you hurt yourself that many times and not figure it out sooner? & you are not wrong. However, my moronic nature has become so frustrating to me that I have finally written down what it takes to not be a moron, so please take these words from this moron seriously, because I know the terrain. I finally know how to not be a moron. In rock climbing.